1. Field of the Invention
The present invention generally relates to a heating flange and more specifically to a heating flange for preheating air in an intake line leading to an internal combustion engine.
2. Description of the Related Art
Presently, for instance in diesel engines, the use of pre-swirl chambers is normally dispensed with to a large extent, and the preheating time can be reduced markedly by means of direct fuel injection under high pressure. In the case of lorries, preheating is normally dispensed with completely, and the temperature required for igniting the fuel is here achieved by strong air compression. This technique depends, however, to a high degree on the temperature and the density of the combustion air taken in. At low temperatures, the electric starter must rotate the engine until a temperature rise has taken place in the combustion chambers due to a plurality of compression processes and until ignition of the fuel is possible. Vehicles which are often operated at low temperatures and low air pressures are therefore equipped with systems heating the intake air prior to the starting operation. At present, such systems operate e.g. on the basis of gas burners.
These systems are, however, disadvantageous insofar as the content of the oxygen required for the future combustion of the fuel is reduced and that, in addition, the technical expenditure is comparatively high.
Hence, alternative electric heating systems are used, this kind of systems being disclosed e.g. in DE 100 26 339 A1 or in DE 195 15 533 C2. In particular the device for preheating air in an intake line leading to a diesel engine, which is shown in DE 100 26 339 A1 and which is provided with a switching unit controllable by means of a semiconductor device operating in a wear-free manner, permits the heating flange to be switched on and off an arbitrary number of times and at very short intervals, i.e. with comparatively high frequencies. Hence, the power of the heating flange can be adapted to the warm-up conditions of the internal combustion engine almost steplessly.
This preheating device is, however, problematic insofar as, due to the high currents flowing (up to 400 ampere and more), the heating flange has to satisfy very special requirements with respect to current endurance, temperature resistance and mechanical stability.